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Plant Quarantine Programs Managed

by APHIS-PPQ

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The quarantine programs for the various crops processed by the Plant Germplasm

Quarantine Program (PGQP) are listed below with a short description of how each

functions.

For general questions or information about the PGQP, contact Joseph Foster (Permit

Holder) at joseph.a.foster@usda.gov.

Bamboo Clones and Seed

Contact: Bishwo Adhikari

Email: bishwo.n.adhikari@usda.gov

Clonal bamboo is usually imported as clumps that include stems with a few to

several nodes or sometimes as plantlets in tissue culture. The quarantine for clonal

bamboo if healthy is one year during which the plants are inspected during growth

and tested twice for viruses, phytoplasmas, and undescribed pathogens. Tests

include leaf dip assay via electron microscopy, ELISA serology, PCR, and highthroughput sequencing (HTS). Infected clones are discarded. Introductions that test
negative for pathogens are released from quarantine and distributed as whole plants

to importers.

Alternatively, bamboo may be imported into the U.S. as seed. Bamboo seed is

treated to control bacteria and fungi, germinated in seed trays, and eventually

potted. These seedlings are also observed for disease symptoms and insect pests

and tested for viruses, phytoplasmas, and undescribed pathogens by ELISA serology,

PCR, and HTS. Symptom-free plants that test negative for the various pathogens are

released from quarantine for distribution as whole plants.

Cassava Clones (Manihot)

Contact: Ronald French

Email: ronald.d.french@usda.gov

Cassava plants for propagation are usually imported as tissue cultures but may

arrive as bare-rooted plants. During growth, the plants are tested for pathogens by

mechanical transmission to sensitive indicator plants, grafting to a sensitive cassava

cultivar, ELISA serology, PCR, and HTS. Infected cassava is subjected to meristem tip

culture and heat therapy, and then the resulting plants are retested to ensure the

elimination of the pathogen(s). This therapy treatment usually adds one year to the

quarantine period. Cassava accessions are shipped to each recipient as 3–4 in vitro

plantlets per clone.

Grass Clones and Seeds

Contact: Bishwo Adhikari

Email: bishwo.n.adhikari@usda.gov

Grass clones may arrive as whole plants, rhizomes, sprigs, stools, canes/stems, or

plantlets in tissue culture from all countries. The growing plants are inspected for

fungal or bacterial pathogens and tested twice a year for many exotic viruses and

phytoplasmas. Pathogen tests include mechanical transmission to sensitive

herbaceous indicator plants, leaf dip assay via electron microscopy, ELISA serology,

PCR, and HTS. Infected germplasm may either be destroyed with the approval of the

importer or entered into the therapy program for pathogen elimination by heat

treatment and tissue culture. Grass clones released from quarantine are usually
shipped to the importer as whole plants.

Seeds of certain grasses are prohibited in commercial quantities from certain

countries but can be imported through quarantine. The seeds are sown in spring, the

growing plants are inspected for pests, and the seed of these plants are harvested

and shipped to the recipient. If pests are found, the seed lot is destroyed.

Pome Fruit Clones [Apples (Malus), Pears (Pyrus),

Quinces (Cydonia, Chaenomeles)]

Contact: Oscar P. Hurtado Gonzales

Email: oscar.hurtado-gonzales@usda.gov

Pome fruit clones are usually imported as dormant budwood but could arrive as

bare-rooted plants. Selected buds are propagated on the appropriate domestic virusfree seedling rootstocks. Growing plants are inspected for pests and tested for

different viruses, viroids, and phytoplasmas by PCR and HTS. Provisional or early

releases within 1 year of importation are possible if the tested importation is

negative for all mentioned tests. Importers must obtain a permit from APHIS Plant

Protection and Quarantine (PPQ) to grow provisionally released pome fruits. A final

release is granted after the second round of PCRs and HTS is conducted during the

second growing year and results are negative. Thus, the quarantine period for

healthy pome introductions is a minimum of 2 years. If the introduction is infected, it

is subjected to therapy to eliminate the detected pathogen(s). Therapy is done by

growing the importation in tissue culture followed by exposure to several months of

heat treatment cycles. Then, 0.2 millimeter meristem tips are excised and cultured

in sterile tissue culture media. A small tree is grown from the meristem and

subjected to all testing to confirm the elimination of the pathogen(s). Thus, detection

of pathogens in pomes adds at least 18 months to the quarantine period. Importers

will receive notification via email about the status of their importation after the first

round of testing has been concluded, approximately 8 months after importation and

establishment of small trees. Pome fruits are released and distributed as dormant

budwood from the tested clone.

Potato Clones and True Potato Seed (Solanum)
Contact: Ronald French

Email: ronald.d.french@usda.gov

Potato clones are usually imported as plantlets in tissue culture but may arrive as

cleaned tubers. During growth from September to May, the potato clones are tested

for many viruses, phytoplasmas, bacteria, and potato spindle tuber viroid by

mechanical transmissions to sensitive indicator plants, ELISA serology, leaf dip assay

by electron microscopy, molecular hybridization, PCR, and HTS. Suspicious

symptoms in the imported plant may be investigated by grafting healthy potato

plants with the introduction. Potatoes that are free of pathogens may be released in

spring, 9 months after arrival. Infected potatoes are exposed to chemotherapy and

thermotherapy in tissue culture, meristem tips are grown, and then the resulting

plants are retested to determine the success of the therapy. The therapy process

may add a year or more to the quarantine period. Vegetatively propagated potatoes

from the tested clones are distributed to each recipient as 3–4 in vitro plantlets per

clone.

Samples from each true potato seed (TPS) lot are germinated and grown in a

quarantine greenhouse from September to May. Each sample is inspected during

growth and tested for viruses by mechanical transmission tests to sensitive indicator

plants and potato spindle tuber viroid by molecular hybridization. Selected PCR tests

and HTS will also be used to detect viruses and other potential pathogens. Seed lots

with samples testing negative for pathogens are distributed to recipients in the

spring without the seeds removed for testing purposes. Infected seed lots are

destroyed.

Rice Seeds (Oryza)

Contact: Bishwo Adhikari

Email: bishwo.n.adhikari@usda.gov

Quarantine regulations are designed to prevent the importation of several exotic

seed-borne fungal and bacterial rice pathogens and control the introduction of

certain rice species (Oryza longistaminata, O. punctata, and O. rufipogon), which are

on the Federal Noxious Weed list. Upon entry in spring, the rice seeds are inspected

and treated with hot water (56 °C, 15 minutes) by an APHIS-PPQ inspector at the

Beltsville Plant Inspection Station. Dried and repackaged seed, which serves as the
parental seed, is released to the crop manager. For each accession, at least 30

healthy seeds are dehulled and surface sterilized in a 1.575-percent sodium

hypochlorite solution for 2 hours. After rinsing in sterile deionized water, seeds are

grown in a tissue culture medium (PDA + 0.5x MS) for 2–3 weeks. Seeds

contaminated with fungal or bacterial growth are discarded. Plants from microbefree cultures are transplanted into pots in the greenhouse. These plants are

inspected visually during growth and at least once as seed heads ripen for fungal or

bacterial pathogens. The growing plants are tested for pathogens by HTS. The

quarantine period for imported rice is usually about 12 months. Seeds free of pests

are released in the fall or early winter and shipped to the importer.

Small Fruit Clones (Actinidia, Ficus, Ribes)

Contact: Joseph Foster

Email: joseph.a.foster@usda.gov

Currants and gooseberries are usually imported as cuttings but may also arrive as

bare-rooted plants. Kiwis and figs arrive as dormant budwood or tissue cultures.

Gooseberry cuttings may be grafted onto domestic jostaberry plants to establish

them and promote vigorous growth before rooting cuttings. Dormant kiwi and fig

budsticks are rooted under mist. Kiwis can be grafted on domestic rootstocks.

Growing plants are tested for pathogens by mechanical transmission to sensitive

herbaceous plants, PCR, and HTS. Dormant Ribes buds are budded onto sensitive

currant indicator plants to test for graft-transmissible pathogens. Introductions that

test negative can be released within 2–3 years. Infected introductions are exposed

to therapy procedures involving heat treatment of growing plants or tissue cultured

plants, and then the resulting plants are retested to confirm that the pathogen has

been eliminated. Currants, gooseberries, figs, and kiwis are distributed as barerooted plants.

Stone Fruit Clones and Seeds (Prunus)

Contact: Joseph A. Foster

Email: joseph.a.foster@usda.gov

Stone fruits, which include fruiting and ornamental almonds, apricots, cherries,

nectarines, peaches, plums, and prunes, are usually imported as dormant budwood
but may arrive as cuttings for rooting or bare-rooted plants. Selected buds are

propagated on the appropriate domestically purchased seedling rootstocks. Growing

plants are inspected during growth and tested for viruses, viroids, bacteria, and

phytoplasmas by transmission tests to sensitive indicators, ELISA serology, PCR, and

HTS. Provisional or early release of clones that test negative in the initial testing is

possible 1–2 years after arrival. Importers must obtain a permit from APHIS-PPQ to

grow provisionally released stone fruits. The final release of the tested clone occurs

after all tests for pathogens are negative, usually within 2–3 years of importation.

Infected clones are exposed to heat treatments in tissue culture or growth

chambers, tips are grown, and then the resulting plants are retested to determine if

therapy was successful. Stone fruit clones are usually distributed as dormant

budwood or bare-rooted trees.

Stone fruit seeds are germinated in the fall and winter and then grown in the

greenhouse in spring. Growing seedlings are tested individually for plum pox virus

by ELISA and RT-PCR, and for potyviruses and ilarviruses by RT-PCR. Buds from

dormant budwood from each seedling are budded on GF 305 peach seedlings to

check for various pathogens. Seedlings that test negative are released and sent to

the importer as bare-rooted plants.

Sugarcane and Related Grass Clones (Saccharum)

Contact: Bishwo Adhikari

Email: bishwo.n.adhikari@usda.gov

Sugarcane is usually exchanged as cane setts and occasionally as plantlets in tissue

culture. Setts should reach PGQP by March (southern hemisphere origins) or August

(northern hemisphere origins). Growing plants are observed for symptoms during

each of two growing cycles and tested for bacteria, viruses, and phytoplasmas by

mechanical transmission to sensitive herbaceous plants, serology, culturing

attempts, PCR, and HTS. Additional tests are conducted after cutting back and then

at shipping. The released setts will be taken from mature plants of the tested clones

that were grown from long, hot water-treated cane pieces. The released setts are

subjected to a long hot water treatment before shipping. The quarantine period for

healthy sugarcane clones imported for propagation is usually about 18 months.

Infected clones are entered into the tissue culture program for pathogen elimination,

and then the resulting plants are retested to determine if therapy was successful.
Therapy prolongs the quarantine period for infected sugarcane.

Sweet Potato Clones (Ipomoea)

Contact: Ronald French

Email: ronald.d.french@usda.gov

Sweet potato clones are usually imported as plantlets in tissue culture but may

occasionally arrive as cleaned roots or cuttings. Plants are grown from April through

October in quarantine greenhouses. Growing plants are inspected for pests and are

tested for viruses and phytoplasmas by grafting stem pieces to Ipomoea setosa, by

PCR, and by HTS. Clones that test negative may be released up to 9 months after

testing has begun. Infected sweet potatoes are subjected to meristem tip culture

and heat therapy, and the resulting plants are retested to verify that the therapy

procedure eliminated the detected pathogen(s). This therapy treatment usually adds

1 year to the quarantine period. Sweet potatoes are released and then shipped to

recipients as 3–4 in vitro plantlets per clone.

Woody Ornamentals

Contact: Joseph Foster

Email: joseph.a.foster@usda.gov

During the last 5 years, various prohibited woody ornamentals, including juniper,

pine, spruce, elms, maples, mulberries, barberries, boxwoods, redbuds, oaks,

hibiscus, and some bonsai have been imported by PGQP. Woody ornamentals are

usually imported as bare-rooted plants but may arrive as cuttings that require

grafting or rooting. The inspection and testing requirements vary with each genus.

Barberries only require inspection during growth for evidence of black stem rust of

wheat. Other genera, such as elms and maples, involve inspections during growth

and pathogen tests for viruses, viroids, and phytoplasmas. Plants testing negative

for pathogens are released and shipped to the importer as whole plants.